Is it permissible to work as an engineer for a company in non-Islamic countries (such as Germany) that produces military technologies, and does the religious ruling change if the intention is to use this knowledge to support Islam in the future?

It is forbidden by Islamic law to assist in wrongdoing or to contribute to the spread of corruption, crime, and unjust aggression by any means of assistance, such as promotion, manufacturing, or trade, as Allah Almighty says: (And cooperate not in sin and aggression. And fear Allah; indeed, Allah is severe in penalty). Infidel nations typically use these military technologies for tyranny, colonization, and spreading chaos.

It is not permissible to work in manufacturing missiles for disbelievers, as it constitutes assisting them in injustice. The intention of supporting Islam through this work does not affect the ruling. The ruling for someone who undertakes this work with the intention of learning for the benefit of Muslims differs from the ruling for an employee who uses this intention as a pretext to justify their work.